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### Re^2: How many colors does a rainbow have?

by tilly (Archbishop)
 on Jan 25, 2009 at 02:54 UTC ( #738743=note: print w/replies, xml ) Need Help??

in reply to Re: How many colors does a rainbow have?
in thread How many colors does a rainbow have?

That's actually not true. For instance red and blue are at opposite ends of the spectrum, so you don't get red + blue without green anywhere. That color is pink, and if you look you will see that it does not appear.
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Re^3: How many colors does a rainbow have?
by wfsp (Abbot) on Jan 26, 2009 at 07:32 UTC
I have fond memories of pink.

A customer's newspaper had spot red but they often used pink in their design and therefore three plates were output instead of two - useless. "Don't use pink, we haven't got pink. What you think is pink is 50% red, use that instead." The other 50% being white.

We referred to pink as a tint, A hue produced by the addition of white.

Also, the colour was named after the flower, not the other way around. Pink described the frilly edges as in pinking shears.

Re^3: How many colors does a rainbow have?
by snafu (Chaplain) on Jan 28, 2009 at 18:52 UTC
One cannot expect the naked eye (especially from a distance and through an imperfect picture) to see or not see specific colors or even all of the colors hidden in a rainbow.

I found this:

(PhD physicist responds) The eye perceives six colors in the rainbow. Red, orange, yellow, green, blue and violet. (some people include the violet color of Indigo as a separate color.) But there are also colors in the infrared and ultraviolet present as well. The rainbow is caused by diffuse refraction of sunlight in water droplets. The source of the light is the sun's photosphere. While each atom in the photosphere may emit light at one quantum frequency, the sun is so hot that doppler shifting of the light causes the lines to "fuzz out" so that you see essentially a continuous spectrum of light. The strictly correct answer, would then be, "an infinite number".

I also found Physics in the Arts By P.U.P.A Gilbert, Willy Haeberli - Page 27. I found that to be pretty interesting.

_ _ _ _ _ _ _ _ _ _
- Jim
Insert clever comment here...

But there are also colors in the infrared and ultraviolet present as well.

Isn't this a contradiction? Colo[u]r being those frequencies of light visible to humans... and infra-red and ultra-violet not being among those...?

While each atom in the photosphere may emit light at one quantum frequency, the sun is so hot that doppler shifting of the light causes the lines to "fuzz out" so that you see essentially a continuous spectrum of light.

I might be wrong about this, but isn't the vast majority of the sun's radiation thermal, i.e. blackbody, i.e. continuous in the frequency domain? Yes, there are spectral lines caused by atomic de-excitation, and they are broadened by Doppler shifting due to the temperature of the gas in the sun (amongst other things) but this isn't what the majority of radiation emitted from the sun is.. is it?

Someone help me out here!
why_bird
........
Those are my principles. If you don't like them I have others.
-- Groucho Marx
.......
Isn't this a contradiction? Colo[u]r being those frequencies of light visible to humans...

All of these arguments depend on the definition of "color", and until we all agree on one, there will never be agreement on how many "colors" are in a rainbow.

isn't the vast majority of the sun's radiation thermal, i.e. blackbody

Well, obviously, essentially all of the sun's radiation is blackbody, in that none of it is reflected or transmitted. :-)

blackbody, i.e. continuous in the frequency domain

While blackbody radiation may be continuous theoretically, that doesn't mean that thermal radiators like the sun have continuous spectra in reality.

Brass tacks: Is the solar spectrum continuous or quantified? If the physics PhD says it's continuous, I'll believe him.

Yes, there are spectral lines ... but this isn't what the majority of radiation emitted from the sun is.. is it?

Is there any reason to suppose that the "smoothness" of the solar spectrum is qualitatively different from one part to another? No; In fact, it looks like the roughness is merely proportional to the intensity, across the spectrum. It also appears that whatever "fuzzing out" is happening, it is not enough to completely smooth out the spectrum. Far from it!

Between the mind which plans and the hands which build, there must be a mediator... and this mediator must be the heart.
Colo[u]r being those frequencies of light visible to humans...

If you define colour in terms of what the human eye sees, there are only three of them, four if you count luminosity that's not in any of the three color categories, or throw in tetrochromacy; five if you count both. So yellow, for instance, is not a color if you define it this way. It's a combination of colours (specifically, red and green), or else it's a pigment that absorbs a certain color (blue).

And yeah, the output of the sun is pretty well continuous across the electromagnetic spectrum, so if you define colors as wavelengths of electromagnetic radiation then the cardinality of the set of all colours in the rainbow is aleph-sub-one, the same as the cardinality of the set of all real numbers. I suppose that means the number of colors in the rainbow is actually greater than infinity, if you define infinity in the usual gradeschool way (which comes out in math as aleph-sub-naught, the cardinality of the set of natural counting numbers).

Shouldn't wavelenghts be multiples of the Planck length?
[]s, HTH, Massa (κς,πμ,πλ)
I believe we would need a better theory of quantum gravity to confirm or deny such speculation.
Now I'm seriously curious - why should they?

So far I've never worked with energy scales where quantization of that order of magnitude would matter (10^-9 vs. 10^-35 meter), so I'm curious where that comes from.

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